A : In physical adsorption, heat of adsorption is low i.e., 20 - 40 kJ /mol.
R : On increasing temperature, physical adsorption increases.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion, mark (1)
B. If both Assertion & Reason are true but reason is not the correct explanation of the assertion, then mark (2)
C. If Assertion is true statement but Reason is false, then mark (3)
D. If both Assertion and Resson are false statements , then mark (4)

Answer

To solve the question, we need to analyze the assertion (A) and the reason (R) given in the statement.

### Step-by-Step Solution:

1. **Understanding Assertion (A)**:
- The assertion states that in physical adsorption, the heat of adsorption is low, specifically in the range of 20 - 40 kJ/mol.
- This is true because physical adsorption (or physisorption) involves weak van der Waals forces, which result in lower energy changes compared to chemical adsorption (or chemisorption).

2. **Understanding Reason (R)**:
- The reason states that on increasing temperature, physical adsorption increases.
- This statement is incorrect. In physical adsorption, as the temperature increases, the kinetic energy of the adsorbate molecules also increases. This increased energy can lead to the breaking of the weak van der Waals forces, resulting in desorption (the process where adsorbate molecules leave the adsorbent surface). Therefore, physical adsorption actually decreases with an increase in temperature.

3. **Conclusion**:
- Since the assertion (A) is true and the reason (R) is false, the correct answer is that the assertion is true, but the reason is false.

### Final Answer:
- Assertion (A) is true, and Reason (R) is false.

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